Haemophilus influenzae are divided into two groups of strains, typable and nontypable. Strains which possess a known capsule are typed by the serological reaction of the capsule with reference antisera. Types a-f have been identified. Strains which fail to react with any of the reference antisera are nontypable.
H. influenzae type b (Hib) is the most frequent cause of neonatal meningitis and other invasive infections in the United States (Fraser et al., 1974, Am. J. Epidemiol. 100:29-34). The major incidence of childhood meningitis occurs between the ages of one and five years. Sixty percent of the meningitis cases due to Hib occur in children under the age of two years (Fraser et al., supra).
It is now well established that nontypable H. influenzae also cause diseases including pneumonia, bacteremia, meningitis, postpartum sepsis, and acute febrile tracheobronchitis in adults (Murphy et al., 1985, J. Infect. Diseases 152:1300-1307). In addition, nontypable H. influenzae are a frequent etiologic agent of otitis media in children and young adults. Indeed, about 20 to 40% of all cases of otitis media can be attributed to H. influenzae. Children may experience multiple infections of the same organism since infection confers no long lasting immunity. Currently, chronic or repeat otitis media is treated by administration of antibiotics and, if necessary, by drainage of the inner ear. H. influenzae strains have also been implicated as a primary cause of sinusitis (Cherry J. D. and J. P. Dudley, 1981, in Textbook of Pediatric Infectious Diseases, Feigin and Cherry eds., pp 103-105). Additionally, nontypable H. influenzae cause neonatal sepsis.
Antiserum produced against the capsular polysaccharide of Hib, polyribosyl ribitol phosphate (PRP), has been shown to be bactericidal and protective against Hib (Smith et al., 1973, Pediatrics 52:637-644; Anderson, et al., 1972, J. Clin. Inv. 51:31-88). Anti-PRP antibody, however, is ineffective against nontypable H. influenzae infection.
Currently available vaccines against H. influenzae are all directed against Hib. All are effective by eliciting anti-PRP antibody. Anti-PRP antibody, however, is ineffective against nontypable H. influenzae, which by definition lack the PRP capsule. There is a long recognized need for a vaccine that will protect against nontypable H. influenzae.